Book/Report

FZJ-2019-01685

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Rastertunnelmikroskopieuntersuchungen bei tiefen Temperaturen : die Defektmorphologie einzelner Ioneneinschüsse und Phasenumwandlungen der zweidimensionalen Eisdoppellage auf Pt(111)

Morgenstern, M. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21742

Report No.: Juel-3299

Abstract: The temperature variable Scanning Tunneling Microscope (STM/ 20 K-700 K) was used to measure the surface damage patterns of single ion impacts and to study adsorption, structure and melting of the ice bilayer on Pt(111). The first part of the thesis describes the ion impact data. First, the migration of Pt self interstitials is detected by their appearance at the surface. Thus, the onset temperature of the self interstitial diffusion is determined to be 22 K. The diffusion energy is estimated to be about 50 meV consistent with earlier different measurements. Second, single ion impacts are analyzed. Due to the low imaging temperature, the surface damage of single ion impacts can be observed prior to any annealing except the interstitial diffusion. This allows to compare the impact patterns directly with Molecular Dynamics Simulations (MDS). For this purpose, the surface damage of Ne$^{+}$, Ar$^{+}$, Kr$^{+}$ and Xe$^{+}$(4.5 keV)-impacts on Pt(111) is analyzed. In particular, the number distribution of adatoms per impact (and thus the adatom yield), the radial distribution of the adatoms and the mean size of adatom and surface vacancy clusters are determined. These data show that an increase of the energy density leads to a change of the adatom production mechanism from a linear cascade mechanism (adatom creation by independent collisions) to a thermal spike mechanism (collective flow of Pt-atoms onto the surface). The energy density threshold, above which the spike mechanism determines the adatom production, lies between the energy density of a Ne$^{+}$(4.5 keV)and an Ar$^{+}$(4.5 keV)-impact. This is evidenced by the direct formation of adatom and vacancy clusters, an increase of the adatom yield with respect to the sputter yield and a broadening of the number distributions "adatoms per impact" with respect to a Poisson distribution. The threshold as weIl as the mentioned features of the impact patterns are reproduced qualitatively well by MDS. However, a quantitative comparison between experimental and theoretical data (adatom yield and radial distribution of the adatoms) shows deviations of the order of 50 %. In addition, two other processes presumably due to collective effects in the ionsolid-interaction are found experimentally: An ion induced adatom mobility leading to adatom cluster formation at higher fiuences and the formation of bulk vacancy clusters. The first takes place at energy densities corresponding to a Ne$^{+}$ (4.5 keV)-impact, i.e. at lower energy densities than the thermal spike determined adatom production, while the second takes place at higher ion energies and masses (Xe$^{+}$ (6.5 keV)). A further increase in ion energy (Xe$^{3+}$ (15 keV)) and a reduction of the melting temperature of the crystal (Au(111)) increase the adatom yield consistent with the idea, that both, higher ion energy and lower melting temperature, lead to an increase in the size of the molten volume during the thermal spike. Two additional investigations concerning the ion-surface interaction have shown that: [...]

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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